Coke-water separator method



United States Patent Inventors John Van de Velde Long Beach; Leonard D. Kosonen, Anaheim, Calif. Appl. No. 782,939 Filed Dec. 11, 1968 Patented Dec. 29, 1970 Assignee Atlantic Richfield Company Philadelphia, Pa. a corporation of Pennsylvania COKE-WATER SEPARATOR METHOD 2 Claims, 3 Drawing Figs.

U.S. Cl 210/170 Int. (I E02b 8/02 Field of Search 52/ 192,

196, l97;2l0/l70 [56] References Cited UNITED STATES PATENTS 3,342,352 9/1967 Sackett, Sr. 52/l92X 3,392,833 7/l 968 Baillie 2 10/1 70X Primary Examiner-Reuben Friedman Assistant Examiner-T. Av Granger Attomeys-Robert .l. Mawhinney and Robert R. Cochran ABSTRACT: A coke-water separator method including a water settling basin and a coke pit separated by a retaining wall having specifically dimensioned passageways therethrough is disclosed. The passageways through the retaining wall are designed such that a line intersecting the edge of the basin and the top of the passageway on the coke pit side of the wall forms an angle with the bottom of the passageway approximately equal to the angle of repose of drained coke. The concept is of general application.

COKE-WATER SEPARATOR'METIIOD BACKGROUND OF THE INVENTION 1. Field of the Invention. 1 I I petroleum coke. Details of the petroleum coking process may be found in any standard treatise on petroleum refining, see, e.g., Bland and Davidson, PETROLEUM PROCESSING HANDBOOK, McGraw Hill, New York, 1967 and Gruse and Stevens, CHEMICAL TECHNOLOGY OF PETROLEUM, McGraw Hill, New York, 1960. In very generalterms, the coking process may be described as a destructive distillation of a petroleum or petroleum-like material which produces fluid components and a solid componennthe latter being referred to as coke." In such processes, it is common to utilize large quantities of water either during the coking operation .or subsequently thereto as a vehicle for removing the coke from the cokingvessel. The result is that the coke is produced in the form of a coke-water mixture oftencontaining more than 50 percent water.

ltis known in the prior art to dump this coke-water mixture into a large settling pit, commonly referred to as a coke pit.

Adjacent the coke pit a settling basin for the water is provided.

drains from the coke pit, to drop the particulate matter carried therein to the bottom of the settlingbasin. Normally the water is recirculated to the coking'system. A retaining wall provided with a pluralityof passageways for drainage therethrough is positioned between the settling basin and thecoke pit. In a known design, the settling basin comprises a maze in which the water flows very slowly from one side ofthe basin to the other and back", etc., around a series of walls extending across a major portion of the basin. A series of weirs and baffles may be provided to aid in the settling of particulate matter from the water to the-bottom of the basin. Thebasin is cleaned tip periodicallyto remove the solid matter. t

In the past, the passageways through the retaining wall,

often referred to as rat holes, were made comparatively small,

for example 6 inches in width and 12 inches in height through a wall 2 or3 feet in thickness at the base. These passageways obviously were large enough to permit drainage of large amounts of water and were believed to be large enough to prevent being plugged, except in most extraordinary situations by single chunks of coke. Nevertheless, the system was completely unsatisfactory.

These passageways, rat holes, consistently plugged very rapidly preventing the drainage of water-from the coke pit to the settling basin. Each time a passageway was unplugged, water heavily laden with coke fines would jet into the settling basin. The liquid in the settling basin normally had the appearance of a thin, black mud. With these heavy loads of particulate matter, the settling basin was quite'ineffective to remove the particles and as the water was recirculated to the coking system extremely high rates of erosion of the pump impellers, conduits, and the fluid handling system generally would begin to plug up again and over a comparatively short period of time, a few minutes, forexample, the passageway The purpose of the settling'basin is to .permit the wate'nas it would be completely clogged again. The fluid which, under pressure from the liquid head inside the pit, shot from the passageway was a thick slurry of coke and water which merely added to the solids content in the settling basin and the erosion and other handling problems inv the liquid system.

Efforts were made to use various types of screens, drain standpipes, etc. but all such attempts were unsuccessful. Attempts were made to manipulate the coke disposition in the pit to provide for adequate drainage through the small passageways in the retainingwall but these attempts were only moderately successful in permitting drainage and generally resulted in the passage of large quantities of coke into the water settling basin. I I In the prior art it has been considered that if the size of the passageway through the retaining wall was increased, perhaps better drainage would result in that-larger chunksof coke could flow with the liquid through the passageways to the set-' tling basin. This result obviously is unsatisfactory. It has now been discovered, contrary to prior thinking, that if the sizes of the passageways through the retaining wall are very greatly increased and are designed in accordance with the principles set forth hcreinafter, highly efficient drainage of the water from the coke pit to the settling basin is possible and that such water as is drainedfrom the coke pit to the basin is substantially free of all but microscopic particles of coke.

SUMMARY or Tris INVENTION f It has now been discovered that if the passageway through the retaining wall is designed such that the plane of the bottom of the passageway and a line intersecting the edge of the water basin and the upper edge of the passageway on the coke pit side of the retaining wall is not greater than the approximate design for systems for the separation of water from solid-water mixtures generally and'an improved method for said separation.

A more specific object of the invention is to provide an improved system and method for separating water from petroleumcoke.

An additional object of the inventionisto provide design criteria for solid-water separationsystems.

An additional specific object of the invention is to provide a retaining wall having passages of particular dimension.

A still more specific object of the invention isto provide a system including a water-solid pit, a water settling basin, and a retaining wall having passages therethrough wherein the passages are of particular design with respect to the angle of repose of a water-solid system and an improved method of separation employing this system.

Still more specifically, an object of this invention is to provide an improved petroleum coke-water separating system comprising a coke pit and a settling basin separated by a retaining wall having passageways therethrough of particular design with respect to the angle of repose of drained petroleum coke and an improved method of separation employing this system. I

The specific arrangement constitutes an additional highly specific and non-limiting object of the invention.

Other objects of the invention will be apparent from the specification which follows and from the drawing to which reference isnow made.

BRIEF DESCRIPTION TI IE DRAWING FIG. 1 is a side view shown'in vertical cross section and perspective of the system of th s invention.

FIG. 2 is an enlarged view of a vertical cross section of one configuration of the retaining wall and the passageway of this invention showing the dimensional and angular relationships.

FIG. 3 is an alternative embodiment of the retaining wall and passageway of this invention showing the critical dimensional and angular relationships.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Without limiting the invention reference is now made to FIG. 1 for a general discussion of the invention in a particular environment and illustrating a specific embodiment.

As illustrated in FIG. I, the system of this invention comprises four major portions or sub-systems, the coke pit 10, the retaining wall l2vhaving. apertures therethrough, the settling basin l4 and the water recirculation or handling system I6,

The coke pit in a particular embodiment comprises a generally rectangular tanklike pit defined on one side by the retaining wall 12. The other walls may be solid or may include apertures according to the design described hereinafter. The

. .coke pit, in operation, contains a solid component 18, inithe particular embodiment the solid is petroleum coke, and a liquid component 20 which in the particular embodiment is water. As previously described, the coke and water mixture is dumped into the coke pit from the'coke manufacturing equipment and it is necessary that the water be separated from the coke. conventionally, this separation occurs in the system It is bbviously desirable to drain the maximum possible quantity of water from the coke in'the coke pit to the settling basin. It is also obviously desirable that the water drained from the coke pit carry an absolute minimum amountiof solids. It is the object of this invention' to accomplish ,th'se desired Petroleum coke is comprised ofsolid particles which range from microscopic individual particlesto chunks several inches in diameter and on occasion few v feet in diameter. The average maximu n diameter of the' kec hunks, however, is

about l5 inches. During manufactii r eruhusually large chunks of coke tend to be deposited ori' the top of the coke pile and are easily removed or broken up. i

v Dry coke 'has an angle of repose of about 30 while, at the upper extreme, wet coke, coke from which water can be 'rem'ovedby mild pressure such as squeezing, tends to be a thick slurry which flows and has an angle of repose, if any, of

'"les's thaii about 5. Between'these extremes, therefis great variability of angle of repose depending upon the degree of wetness. For example, damp'cok, coke which feels wet to the touch but from which water canhot be removed by mild pres- 1 sure, has an angle of repose on the order of 60 while drained coke, which contairi s between about percent and about L percent water has an angleof repose'onthe order of about :22. The angle of repose for present purposes may be defined as that angle, with respect to the plane 'on' which the material is =-.described in this invention. The coke, when it has been I width, w, and a height, h, extending through the thickness, t,

of the wall. These passageways 26 are normally located at the base of the wall but may be located at a point above the base of the wall depending upon design requirements and criteria not here relevant. In the particular embodiment shown, the passageways are located at the base of the wall and are of uniform width and height through the thickness of the wall. This latter requirement is not necessary and the height on the rear side of the wall 22 may be either greater or lesser than the height of the passageway on the front side of the wall adjacent the coke pit, the latter height being the important dimension insofar as this invention is concerned.

The settling basin I4 is, in a preferred embodiment, comprised of a series of channels, the first of which is shown at 28. As the water is drained from the pit l0 through the passageways 26 it flows into the first of the channels 28 and some of the solid matter settles to the bottom 30 of this channel. The water flows around'the end of the separating wall 32 to the channel 34 which may be provided with a weir 36. From channel 34, the the water flows around the end of separating wall 38 and over another weir 40 and, if desired, under a baffle 42 in channel 44. The water then flows around separating wall to the recovery pit 48 from which the water is pumped by means of the recirculation system 16; Recirculation 16 includes an intake conduit 50, a pump 52 and a distributing conduit 54.

' The design of the settling basin as shown and described is exemplary of the types of channels, weirs, baffles, and pits, etc. which may be provided in the basin. The number of channels, weirs, baffles, etc. are determined according to the quantity of water to be handled, the amount of solids in the water, and the desired clarity of the water in the pit. The particular design of the settling basin is not critical to this invention and any settling basin may be used without departing from the invention.

laying, which is formed by the slope of a pile of the material lying at rest on the plane. 4, -For reasons which will be obvious,'it is inefficient in a commercial operation to "permit the coke to reside in .the coke pit long enough'to produce dry coke. Most efficient operation dictates that the coke be drained of free water and removed'tp other facilities for further d'ryin'gfif this is desired. Ag-

cordingly, it is the object of this invention to provide a means for efficient drainage of solid material such as petroleum coke.

Ithas now been'found, contrary to the experience and beliefs of the prior art as described hereinbefore, that within limits to be described the use of a larger passageway through "the retaining wall riot only does not increase the solids content of the liquid flowing therethroughbut in fact permits free drainage of substantially clear water from the coke pit. This phenomena is best described by reference to FIG. ,2. In F1632,

the retaining wall 12 the'edge pfthe water settling basin 14 are shown. The height 'of the passageway adjacent the 'so'lidspit, h, and the distance from the inside surface of the retaining wall to ithe edge of the basin, d, are indicated. An imaginary line, a, is shownintersecting t'he edge of the water basin 14 and the upper edge of the passageway 26 on the front surface of the wall, 12 adjacent the solids pit. The line a forms an angle 4) with the plane of the base of the passageway 263).

It has now been discovered that if the height h is so dimensioned that the angle between tlie imaginary line a and the base plane 11 is not greater than the approximate angle of repose of the drained solid in the pit, then the liquidwill flow relatively freely thr ough'the solid, through the passageway and into the settling basin carrying very low levels of solids therewith and'that most of the solids carried are microscopic in size. Preferably, for efficient design, the angle (b is appiioxir mately equal to the angle of repose of the drained solid. lnfthe case of petroleum coke in the environment tested, the angle tie a PigxLa x equal to 2.?" .5325. e e was ga b tively uniform manufacturing process there is some variability in the nature of the coke, the angle may range from about.l8 or l9 to about 25 or 26, Obviously, a different angle would be required using different solids and liquids. The cross s-cictional diameterof the passageways, must be larger thanthe average maximum diameterof the individual solid particlesgor chunks. ln.the case of petroleum coke, the minimum vertical or lateral diameter is, therefore, limited to about l5 inches.

As indicated, the most efficient design criteria suggests that the angle 9') be equal, or approximately equal to the angllepf repose of the drained solids involyed. Obviously equivalent resultsmay be obtained by using an angle which'is not greater than the approximate angle of repose. For example, an equivalent design would be to extend a ledge, as in the case of FIG. 2, to the edge of the settling basin beyond that required by the foregoing design criteria. In this case, the solid would merely repose in the passage and as the water drained out it would merely flow across the upper flat surface of the ledge and then into the pit.

The thickness of the wall per'se, insofar as this invention is concerned, is of no consequence and will be determined by other design criteria, such as the height of the wall, the height of head in the pit, the strength required, the materials used, etc. In practice, a concrete wall several feet in height and from 2 to 3 feet in thickness at the base has been found satisfactory.

An alternative embodiment is shown in FIG. 3 wherein the thickness of the base d is such that the edge of the basin coincides with the bottom edge of the outside surface of the wall. Clearly, by appropriate design considerations thicker or thinner walls may be used depending upon considerations not relevant insofar as the invention is concerned.

As illustrated in the FIGS. the passageway 26 is uniform in dimensions through the thickness of the wall. In design, this is a convenient method of forming the passageway in the wall and provides for convenient cleaning of the passageway on such rare occasions as plugging may occur as a result of abnormal operation. It is not necessary, however, that the passageway be uniform in dimension. For example, the

passageway may slope from the inner wall downwardly to the was designed according to the configuration of FIG. 3 wherein the height h is equal to about 22 inches and the angle 4) is equal to about 22. The coincidence of these numbers is not, however, significant. The base of the wall was made somewhat thicker than minimum requirements to provide additional strength at the base.

The angle 4), it has been found, may be slightly greater than the angle of repose but should not be greater than about 25 or 26', where the angle of repose is 22. Stated differently, the line a intersecting the edge of the basin adjacent the wall and the top of the passageway on the coke side of the wall should form an angle with the bottom of the passageway of not greater than approximately the angle of repose of the drained petroleum coke in the plane of the bottom of the passageway.

The width of the passageways must be greater than the average maximum solid particle diameter and is limited by the strength considerations in the design of the wall. In the particular embodiment constructed, following experimentation, the width of the passageways was 30 inches and a plurality of spaced passageways arranged across the base of the wall were formed.

While the invention has been described with particular reference to a system for separating water from petroleum coke it will be readily realized and understood that the system is of more general application. The system and the design criteria described hereinbefore may be used wherein any free flowing liquid is to be drained from. any solid which, when drained, has a definite angle of repose. The system is not particularly advantageous with certain types of solids, for example, large particles of silicate gravel of approximately uniform size, since such materials readily drain and the particles in the body of the solid do not have a significant coherency when wet. Where the particles of the solid tend to cohere when wet and tend to flow when the liquid content is high, however, the system of this invention is especially advantageous.

In practical operation, it has been found desirable to provide a mound of petroleum coke, as indicated at 18 in FIG. 1, adjacent the wall somewhat higher than the average level of coke in the pit to prevent the level of water, which tends to pool as shown at 20, from being higher than the coke at the front surface of the retaining wall 12. In practice, it has been found desirable to maintain this mound at a minimum thickness, measured laterally from the front surface of the wall, of about 8 feet and a minimum height of about 15 feet. This arrangement of the coke permits free drainage from the body of the coke-water mixture in the pit to the settling basin and prevents both plugging of the passageways according to the design of this invention and washing of mixtures of water and coke through these passageways. The latter can occur if the water is permitted to puddle against the retaining wall.

The efficiency of this process is readily apparent from observation. Before the installation of a retaining wall according to the design described, the liquid in the settling basin was, as previously indicated, of the consistency of a very thin black mud carrying very high concentrations of solid materials suspended therein. The maze provided was insufficient to permit complete, or even substantially complete settling of the solid particles and it was necessary at frequent intervals to clean the settling pit of the settled solids. This was obviously an expensive and time consuming operation. In addition, the wear rates on the impellers in the pumps and in the other fluid handling systems were exceedingly high and replacement was frequently necessary.

Following installation of the invention as described, the water draining from the pit into the settling basin was substantially clear. The water in the settling basin is, on an average, about 6 to 8 feet in depth. To the eye, the water is perfectly clear and on the bottom, which is readily seen from 20 or 30 feet above the water surface, there is only a thin, partial layer of coke particles. These particles are of the consistency of fine sand. While the water appears to beclear, it does contain small quantities of microscopic solid particles. Consequently, there is still a very slight amount of wear on the pump impellers but replacement of these parts and other parts of the fluid handling system has been reduced to practically nil.

This efficient drainage system has resulted in enormous savings in terms of replacement parts and labor. The cost of labor for replacement has been reduced to practically zero and the manpower required to maintain the drainage system in operation has been greatly reduced. In addition to these benefits, the coke removed from the drainage pit is of more consistent moisture content and is more easily screened, sorted, stored and otherwise handled.

As will be apparent to one skilled in the art from the foregoing, the invention as described provides highly desirable and unexpected results and permits very substantial savings of time and labor in the production and handling of petroleum coke and in the drainage of liquids from solids generally. It will be understood also that the invention is not limited to the specific embodiment or application described hereinbefore and that departures from the specific embodiments and illustrations may be made without departing from the spirit and scope of the invention.

We claim:

1. A method for separating petroleum coke and water which comprises:

a. placing the mixture of coke and water in a coke pit;

b. retaining the mixture in said coke pit by means of a retaining wall erected so as to separate said coke pit from a water settling basin, said retaining wall having at least one drainage passageway therethrough;

c. permitting drainage of water from said coke pit to said water settling basin through said passageway; but

(1. not permitting passage of said petroleum coke to said water settling basin, said drainage passageway being so constructed and disposed that a line intersecting the edge of the basin adjacent the wall and the top of the passageway on the coke pit side of the wall forms an angle with the bottom of the passageway of not greater than approximately the angle of repose of drained petroleum coke in the plane of the bottom of the passageway.

2. The method of claim 1 wherein the vertical and lateral dimensions of said passageway are each greater than about 15 inches. 

